Microelectronic circuits use metallization for a wide range of purposes. For example, metallization may be used to electrically interconnect the various components on a workpiece, such as the components formed in a semiconductor wafer. Further, the metallization may be used to form the actual electronic components on the workpiece. Such components include, for example, read/write heads, waveguides, inductors, etc.
There are a wide range of manufacturing processes that may be used to deposit the metallization on the workpiece in the desired manner. Such processes included chemical vapor deposition, physical vapor deposition, and electroplating. Of these, electroplating is often preferable since the capital and the operating costs of electroplating are generally less than other metallization processes. Electroplating can take place at ambient temperatures and ambient pressures. As such, strict control of the ambient temperature and pressure conditions is unnecessary.
Electroplating of workpieces that are used to form microelectronic circuits generally takes place in a reactor. One such reactor is illustrated generally at 2 of FIG. 1 and is described in more detailed in U.S. Ser. No. 08/988,333 filed Sep. 30, 1997, now U.S. Pat. No. 5,985,126 entitled "Semiconductor Plating System Workpiece Support Having Workpiece--Engaging Electrodes With Distal Contact Part and Dielectric Cover", the teachings of which are hereby incorporated by reference. As shown in FIG. 1, the reactor 2 generally comprises a rotor head 3 that supports the workpiece 4 so that the side of the workpiece to be processed (front side) is disposed to contact the upper surface of a plating bath 5 that is held in a reservoir 6 or the like. In this position, only the front side of the workpiece 4 contacts the plating bath 5 while the back side (side of the workpiece that is not to be processed at that time) preferably does not contact the plating bath. An anode assembly 7 is disposed in the plating bath 5 and is connected to a positive potential terminal of a plating power supply 8. A plurality of finger contacts 9 or the like contact the front side of the workpiece 4 and serve to electrically connect the workpiece 4 to a negative potential terminal of the plating power supply 8. In operation, the plating power supply provides an electrical potential difference between the anode and the workpiece which results in a chemical plating reaction at the front side of the workpiece in which the desired metal is deposited.
Although the foregoing reactor construction is suitable for many microelectronic electroplating applications, the present inventors have recognized that such a construction may be a disadvantage in other applications. These disadvantages are generally associated with the finger contacts. To electroplate a workpiece, electrical contact must be made with the surface of the workpiece to be plated. Usually only the active, front side of the workpiece is electrically conductive, and it is this surface to which electrical contact is made. Consequently, when the workpiece 4 is disposed so that it is in contact with the plating bath, the finger contacts 9 are also submerged in the plating bath. As such, the finger contacts 9 must be constructed to withstand the wet and harsh conditions of the plating bath environment. Construction of such contacts can be quite costly. For example, to withstand the environment, the finger contacts 9 may be constructed so that they have a platinum core that functions as the conductive portion of the finger, and an exterior skin that is comprised of titanium and a dielectric material such as PVDF. Even when such costly materials are used, the contacts may not be completely resistant to degrading in the plating bath. If the finger contacts are unable to withstand the plating bath environment over time, they will gradually degrade and become ineffective as conductive contacts. Further, such degradation may result in the introduction of contaminants into the plating bath, even before contact degradation is visibly apparent.
Other problems are also associated with this front side contact geometry. Making electrical contact to the front side of the workpiece usually involves complicated mechanisms which negatively impact reliability of the overall apparatus. A further potential problem results from the fact that plating takes place at an accelerated rate proximate the finger contacts. This accelerated deposition results in non-uniformly of the metallization as measured across the entire surface of the workpiece. As the microelectronics industry drives toward further miniaturization of microelectronic devices, such non-uniformities cannot be tolerated.
The present inventors have thus recognized that it would be advantageous in certain processes to provide an apparatus for electroplating a workpiece which reliably makes electrical contact to a back side (side not then in-process at the processing station) of the workpiece yet can electroplate the front side. The present inventors have also recognized that it would be advantageous to provide a back side contact which would simplify part design, reduce material costs, and improve apparatus reliability.